Government regulations and market demands continue to emphasize conservation of fossil fuels in the transportation industry. There is therefore an increasing demand for vehicles which are fuelled, either exclusively or partly with fuels from renewable or bio-derived sources (e.g. biodiesel fuels).
It is known to include fatty acid alkyl esters (FAAEs), in particular fatty acid methyl esters (FAMEs), in diesel fuel compositions. FAME is produced via a chemical process called transesterification with methanol in the presence of a catalyst to yield methyl esters. FAME can be produced from various oil-derived feedstocks such as soybean, rapeseed, sunflower seed, coconut and used vegetable oils. FAAEs may be added for a variety of reasons, including to reduce the environmental impact of the fuel production and consumption process or to improve lubricity.
However, it has been found that the lubricant oil compositions used for lubricating an internal combustion engine can often become diluted with the biofuel which is used to fuel the engine. Biodiesel fuels include components of low volatility which are slow to vaporize after injection of the fuel into the engine. Typically, an unburnt portion of the biodiesel and some of the resulting partially combusted decomposition products become mixed with the lubricating oil composition on the cylinder wall and are washed down into the oil sump, thereby contaminating the crankcase lubricant. The biodiesel fuel in the contaminated lubricant may form further decomposition products due to the extreme conditions during lubrication of the engine. In particular, it has been found that dilution of a lubricating oil composition with a FAAE, such as a FAME, can lead to an undesirable effect on a lubricating oil composition's ability to control oxidative stability and to maintain base number. The presence of olefinic double bonds and ester functionality in the biodiesel results in the biodiesel fuels being susceptible to oxidative degradation and renders the lubricating oil composition oxidatively unstable and more susceptible to increase in acid number (TAN), reduction in base number (TBN) and sludge and deposit formation. Oxidation of FAME in the sump leads to the formation of acids. If not neutralised, these acids can cause corrosion. If neutralized by a base containing a metal counterion, they can form sludge. Additionally too much base used in an attempt to neutralise acid formation can lead to ash formation on the DPF. The higher the biodiesel contamination in the oil the lower the oxidative stability of the lubricating oil composition.
Moreover it has been found that this problem of reduced oxidative stability is significantly worse in diesel engines which employ a late post-injection of fuel into the cylinder (e.g. light duty, medium duty and passenger car diesel engines) to regenerate an exhaust gas after-treatment device. This mode of after-treatment device regeneration can lead to higher levels of FAME dilution in the oil.
Accordingly, it would be desirable to provide a lubricating oil composition for use in the crankcase of an internal combustion engine which has improved base number retention and acid number retention, both in the presence or absence of biofuels such as FAME. In addition, it would also be desirable to provide a lubricating oil composition which provides such improved base number retention and acid number retention, without leading to ash formation on the DPF.
It would also be desirable to provide a lubricating oil composition for use in the crankcase of an internal combustion engine which reduces the loss in oxidative stability which can occur when the internal combustion engine is fuelled with a biofuel such as a biodiesel. In addition, it would also be desirable to provide a lubricating oil composition which reduces such loss in oxidative stability without leading to ash formation on the DPF.
Verkade bases are compounds having a football-shaped proazaphosphatrane molecular structure of formula (1) below:

Verkade bases are very strong bases due to the extraordinary stability of the protonated species which is formed when (1) reacts with a proton. Due to the stability of the protonated form, Verkade bases are about eight orders of magnitude stronger as a Lewis base than any amine known.
Verkade bases have been successfully applied in a variety of organic reactions, such as alkylations, dehydrohalogenations, acylations, a variety of condensation and organometallic reactions for carbon-carbon bond formation. A second characteristic of Verkade bases of formula (1) is their ability to act as a superior catalyst for a continuously widening range of reactions such as protecting alcohol groups with various silyl groups during multistep synthesis, trimerizing isocyanates to isocyanurates and the synthesis of alpha, beta-unsaturated nitriles.
It has now surprisingly been found by the present inventors that Verkade bases can be used to improve base number retention and acid number retention of a lubricating oil composition for the crankcase of an internal combustion engine, in particular wherein the internal combustion engine is fuelled with a biofuel composition, in particular a biofuel composition which comprises a fatty acid alkyl ester.
Verkade bases could also be used to reduce the loss in oxidative stability of a lubricating oil composition for the crankcase of an internal combustion engine, wherein the internal combustion engine is fuelled with a biofuel composition, in particular a biofuel composition which comprises a fatty acid alkyl ester.